Technical Field
Some embodiments of the present invention relate to a forging method and a forging apparatus that performs forging while applying ultrasonic vibration to a die.
Description of the Related Art
The following description of related art sets forth the inventors' knowledge of related art and certain problems therein and should not be construed as an admission of knowledge in the prior art.
Conventionally, ultrasonic forging is publicly known in which ultrasonic vibration is applied to a shaping die during the shaping operation in performing forging. In the ultrasonic forging, as described in a Non-Patent Document (Masahiko Jin, “Fundamental Study on Ultrasonic Micro Coining (Ver. 4).” “56th Plastic Shaping Association Lecture Presentation Lecture Collection of Paper.” 2005, p. 583-584” or Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2009-279596), it is possible to decrease a shaping load and/or improve a shape transfer property.
Such a forging apparatus for performing ultrasonic forging is provided with a die assembly including a die and a punch, a vibrator attached to the die, and an ultrasonic vibration device that drives the vibrator. At the time of applying a pressure to a forging material in the die with the punch, the vibrator is driven by the output from the ultrasonic vibration device to apply ultrasonic vibration to the die.
On the other hand, in the aforementioned forging apparatus, it is adjusted so that the vibrator is driven at the resonance frequency of the die by the ultrasonic vibration device. For example, as described in Patent Document 2 (Japanese Unexamined Patent Application Publication No. 2000-42490), Patent Document 3 (Japanese Patent No. 2681603), etc., an ultrasonic vibration device is provided with a tracking function. An initial value (reference frequency) of the vibration frequency by the ultrasonic vibration device is set near the resonance frequency, and the vibration frequency is converged to the resonance frequency by the tracking function to vibrate the die in the resonant condition.
By the way, when the present inventors were performing ultrasonic forging using the aforementioned forging apparatus, it was confirmed that there is a case in which the die does not vibrate at the resonance frequency and does not vibrate with a sufficient amplitude regardless that the ultrasonic vibration device is equipped with a tracking function. As a result, this caused problems that it was difficult to, for example, assuredly decrease the shaping load and improve the shape transfer property (formability of minute shape).
The description herein of advantages and disadvantages of various features, embodiments, methods, and apparatus disclosed in other publications is in no way intended to limit the present disclosure. For example, certain features of the preferred described embodiments of the disclosure may be capable of overcoming certain disadvantages and/or providing certain advantages, such as, e.g., disadvantages and/or advantages discussed herein, while retaining some or all of the features, embodiments, methods, and apparatus disclosed therein.